We have a long standing interest in understanding how inflammatory edema alters vascular and epithelial barriers. These barriers are dependent on the focal apposition of the cells to each other and to the underlying matrix. Our recently published work indicates that some agonists initially decrease endothelial and epithelial barrier function without increasing tension within the cells. More recent work indicates that histamine initially decreases focal apposition of HUVE cells at sites of cell-cell ahesion (measured as the impedance of a layer of cells on an electrode). In other recent work we found that the tyrosine phosphatase inhibitor, bPVphen, increases focal apposition of MDCK cells at cell-cell sites. This is associated with tyrosine phosphyorylation of E-cadherin. Cadherins are transmembrane proteins which contribute importanty to cell-cell apposition through homotypic binding at adherens junctions. ECV304 cells are a line of endothelial cells that do not express the endothelial cadherin, cadherin-5. When these cells are exposed to histamine they do not decrease focal apposition. When they are exposed to the tyrosine phosphatase inhibitor, bPVphen, they show a slow fall in impedance. In contrast, when the same cells are transfected with E-cadherin or cadherin-5 they show a prompt fall in cell-cell apposition with histamine. When the E-cadherin transfected cells are exposed to bPVphen, cell-cell apposition increases. When the cells transfected with cadherin-5 are exposed to bPVphen, cell-matrix, but not, cell-cell apposition increases, similar to what happens in HUVE cells. These observations implicate important effects of signalling on the cadherin and its uniquely associated proteins. We will use the transfected cells to examine effects of mutations in the cadherins on regulation of adherens junction function, which we can measure in real time.